デバッガみたいに自動でスクロールアップするUITextView

iOS 7 OSD Log

@interface SomeViewController ()
@property (weak) UITextView *logView;
@end

@implementation SomeViewController
- (void)writeOSDLog:(NSString *)log
{
	if (self.logView == nil) {
		NSTextStorage *textStorage = [NSTextStorage new];
		NSLayoutManager *layoutManager = [NSLayoutManager new];
		NSTextContainer *textContainer = [[NSTextContainer alloc] initWithSize:self.view.bounds.size];
		[textStorage addLayoutManager:layoutManager];
		[layoutManager addTextContainer:textContainer];
		
		UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(8, 200, 300, 200)
												   textContainer:textContainer];
		textView.backgroundColor = [UIColor colorWithWhite:0 alpha:0.5];
		textView.textColor = [UIColor greenColor];
		textView.font = [UIFont systemFontOfSize:9];
		textView.editable = NO;
		
		[self.view addSubview:textView];
		self.logView = textView;
	}
	
	NSDateFormatter *logDateFormatter = [[NSDateFormatter alloc] init];
	logDateFormatter.dateFormat = @"HH:mm:ss.SS";
	NSString *string = [self.logView.text stringByAppendingFormat:@"%@ %@\n",
						[logDateFormatter stringFromDate:[NSDate date]], log];
	if (3000 < string.length) {
		string = [string substringFromIndex:string.length - 3000];
	}
	self.logView.text = string;
	[self.logView scrollRangeToVisible:NSMakeRange(string.length, 0)];
}

@end